Science: End of the Meter Bars?

Among science’s most sacred relics are the standard “meter bars” of platinum-iridium that lie in an underground shrine at Sèvres, near Paris. Replacing a babel of medieval units, they originated in the spurt of innovation that followed the French Revolution. The newfangled meter was intended to be one ten-millionth of the distance between the earth’s equator and the North Pole, but difficulties of measurement made the exact length hard to determine. So the meter that was finally accepted (39.37 in. in length) was almost as arbitrary a unit as the ells, feet, rods and pieds de roi that it replaced.

For a century and a half the meter, defined as the average distance between microscopic lines on a master meter bar, was good enough. Then science began to demand more exact measurements. Last week a ten-nation advisory committee meeting at Sèvres recommended that the hallowed meter bars be abandoned in favor of wave lengths of light. Next year a full-dress international conference will make the final decision. It will probably doom the meter bars.

The only decision left will be what kind of light waves to use as a standard. The Germans favor light given off by atoms of a krypton isotope. The Russians prefer cadmium 114. U.S. scientists would like to use mercury 198, which they have been making out of gold in a nuclear reactor.